Wide Pits Research Articles

Failure Analysis of Corrosion Pit on Outer Wall of Membrane Wall Pipe

Abstract Flue gas pipework is a critical component of a flue gas treatment system, mainly transporting the flue gases produced by a combustion plant from the source to the vent. Flue gas pipework is vital in all applications, such as thermal storage gas stoves, heaters, and gas water heaters. However, due to negligent management during the use of piping. Corrosion pits were created in several places on the outer wall of a membrane wall pipe located on the flue gas side of the membrane wall pipe. The external circulation medium of the membrane wall pipe is mainly high-temperature flue gas, and the internal circulation medium is water. This paper determines the causes of the corrosion pits by macroscopic observation, metallographic microstructure analysis, scanning electron microscopy, and energy dispersive spectroscopy (EDS). It was found that the outer wall of the flue gas sidewall pipe of the failed part was covered with reddish-brown rust, wide and shallow corrosion pits were observed, and the detection area of the inner surface of the pits had a high ‘S’ content. To reiterate, it was concluded that the cause of the corrosion pits was the flue gas dew-point corrosion.

Damage evolution and fracture characteristics of coal rock impacted by self‐excited pulse water jet under different stress loading conditions

AbstractIn this paper, based on smoothed‐particle hydrodynamics‐finite element method, numerical models of plunger squeezing water at a sinusoidal velocity were established to simulate self‐excited pulse water jet (SEPWJ). RHT constitutive model was adopted to describe the damage and failure of coal rock impacted by water jet. The morphological evolutions of broken pits and timeliness of rock‐breaking efficiency of SEPWJ and continuous water jet (CWJ) under the conditions with and without stress loadings were obtained and compared. The evolution laws of damage and stress inner coal rock induced by jet impact, and the failure mechanism were revealed. And the influences of different stress loading magnitudes on the fracture characteristics of coal rock were investigated. The results show that the morphologies of broken pits formed by self‐excited pulse jet undergo changes in a semi‐circular, U‐shaped, V‐shaped, and bullet shaped in sequence under the stress‐free loading condition. When applying one‐dimensional (1D) and 2D stress loadings, the shallow but wide broken pits with laminar main cracks along the stress loading direction and the inverted trapezoidal bowl broken pits are formed, respectively. With the increase of 1D stress, the depth and width of broken pits slightly decrease as a quadratic parabolic function and linearly increase, respectively. And the broken pit width and area both show an exponential slow decreasing trends with the increasing 2D stress. SEPWJ can induce higher stresses to cause the earlier occurrence of initial damage and the shorter duration of damage accumulation to coal rock than CWJ, which leads to a better rock‐breaking effect. The surface and deeper coal rock elements are broken mainly due to compressive shear stresses. The 2D stress loading delays the initial damage occurrence and prolongs the damage accumulation duration due to inhibitory effect of stress loading on jet impact.

MORPHO-ANATOMICAL PROFILE OF ELAEOCARPUS TUBERCULATUS ROXB

Objective: The anatomical studies of Elaeocarpus tuberculatus Roxb. (Elaeocarpaceae), an indigenous medicinal plant in the Indian pharmacopoeia. Methods: Fresh leaf and stem samples of E. tuberculatus were scrutinized macroscopic and microscopically by standard procedures. Results: Macroscopically, the leaves are simple, long, coriaceous, and rusty below, base obtuse, margin serrate, apex obtuse and petiole 3 cm long. Microscopically, the leaf showed the presence of four prominent collateral bundles. Paracytic stomata were distributed in the abaxial epidermis whereas the adaxial epidermis was apostomatic. The petiole was four-angled including wing bundles. The stem exhibited fissured periderm, wide secondary phloem, secondary xylem with incipient growth ring and abundant calcium oxalate crystals. Powdered microscopic study of the leaf revealed the presence of long whip-like epidermal trichomes, crystals, vessel elements showing pits and fiber-like sclereids. The stem powder showed thick-walled fibers with wide lumen, narrow fibers and a sclerenchyma cell showing wide pits. Conclusion: The results of the study can serve as a valuable source of information and provide suitable standards for the identification of E. tuberculatus in future investigations and applications

Experimental study on stress and deformation characteristics of foundation pit considering excavation width using 3D printing technology

A sophisticated model of the foundation pit support structure was developed via a model test that incorporated 3D printing technology. A meticulously scaled-down simulation of foundation pit excavation was conducted, utilizing the excavation width of the foundation pit as the sole variable, to evaluate and compare the impact of various foundation pit widths on the force and deformation characteristics of the foundation pit following layer-by-layer excavation. The findings indicate that the stress and deformation characteristics of the retaining structure shift from the “cantilever” mode to a composite mode of “internally convex” or “concave-convex” as the pit is excavated and internal support is installed. The change in pit width has minimal influence on the mechanical response law of the support structure during excavation. Nonetheless, the alteration in the pit width had a direct effect on both the internal force and deformation of the support structure, as well as the change in surface settlement value. In the experiment, wider pits had monitoring values that increased multiple times compared to narrower pits. The width of the foundation pit has a considerable impact on the mechanical response and stability of the pit, which is evident in the relatively lower lateral earth pressure on the outside of the retaining structure in narrower pits. This results in less stress and deformation of the pit structure. Moreover, the decrease in the passive zone of the pit contributes to better stability, indicating that the lower lateral earth pressure on the outside of the retaining structure is an innate reason for the excellent stability of narrower pits.

WITHDRAWN: Investigation on corrosion behaviors of 316 stainless steel in deep-sea water/sediments of the South China Sea via manned deep diving

As observed in a 3404-meter-deep field test via manned diving, 316 SS mainly occurs pitting corrosion in deep-sea water/sediments and corrodes 3-4 times faster than that in shallow sea. In water, due to the synergistic effect of high hydrostatic pressure and Cl− ions, the passive film becomes loose and nonuniform, and the pits expand laterally, leading to wide and shallow pits. In sediments, S2− ions inhibit the re-passivation process and make the passive film thinner, causing numerous pits initiate. Because of the poor Cl− ions transfer efficiency, the pits expand slowly in lateral direction, resulting in vertical pits.

Influence of Friction Stir Additive Manufacturing Parameters on Dry Friction and Wear Properties of Al-Mg-Si Alloy's Built Surfaces Fabricated by Sheet Lamination

Abstract In this article, friction-stir additive manufacturing, a solid-state process for rapid fabrication of large components, is employed to investigate laminated Al-Mg-Si alloy blocks. The study delves into microstructural changes, hardness distribution, and wear behavior on two distinct surfaces using various parameters such as rotational speed (800 and 1200 rpm), traverse speed (41 and 82 mm/min), and a 50% pin overlap for block fabrication. Macrographs demonstrate the influence of adjacent toolpath overlap on layer integrity through interfacial mixing and consolidation of plastically deformed material. Within the overall stirred zone, re-stirring effects lead to refined grain formation and the dissolution of Mg2Si precipitates, resulting in an uneven micro-hardness distribution due to varying thermal cycles. Notably, specimens with a traverse speed of 41 mm/min exhibit reduced wear loss, attributed to microstructural changes that enhance resistance to plastic deformation during sliding, thereby improving tribolayer stability. This enhancement is attributed to increased hardness arising from refined grains and the strain hardening effect. Interestingly, the study finds that the horizontal surface of the fabricated blocks displays superior wear resistance compared to the vertical surface, due to the more homogeneous microstructure in individual layers. Further analysis using FESEM and EDS unveils the presence of glaze layers, oxide films, galling surfaces, grooving, trimming impacts, ploughing marks, and the accumulation of wear debris within wide pits and on worn-out pin surfaces. Scar morphology reveals that both abrasive and adhesive wear mechanisms contribute to volumetric losses in the specimens.

Quantitative analysis of the correlation between geometric parameters of pits and stress concentration factors for a plate subject to uniaxial tensile stress

The offshore environment is inherently corrosive. Consequently, pits may nucleate on exposed steel surfaces. Corrosion pits can be a source of crack initiation when the structure is subject to fatigue loading. The criticality of a corrosion pit with respect to the structural integrity depends on its shape and size and can be quantified using a stress concentration factor (Kt). In this work, a parametric 3D finite element model is developed to perform stress analysis of a pitted plate subjected to uniaxial tensile stress. The model is used for an extensive parameter study in which Kt is determined for various pit configurations. It is demonstrated that each one of the geometric parameters holds a substantial influence on the location of the Most Critical Region (MCR). It is shown that Kt increases as the pit gets narrower. Pits with an elliptical mouth yield higher Kt values when the angle between the load direction and the pit mouth major axis increases. Moreover, Kt increases with the increase in the localized thickness loss which is more pronounced for relatively wider pits. Finally, a regression model is presented for estimating Kt based on the geometric parameters of a pit.

Stress corrosion cracking failure of X80 carbon steel U-bend caused by Desulfovibrio vulgaris biocorrosion

Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris, which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel.

Clinical features and imaging characteristics in achiasmia.

Achiasmia is a rare visual pathway maldevelopment with reduced decussation of the axons in the optic chiasm. Our aim was to investigate clinical characteristics, macular, optic nerve and brain morphology in achiasmia. A prospective, cross-sectional, observational study of 12 participants with achiasmia [8 males and 4 females; 29.6 ± 18.4 years (mean ± standard deviation)] and 24 gender-, age-, ethnicity- and refraction-matched healthy controls was done. Full ophthalmology assessment, eye movement recording, a high-resolution spectral-domain optical coherence tomography of the macular and optic disc, five-channel visual-evoked responses, eye movement recordings and MRI scans of the brain and orbits were acquired. Achiasmia was confirmed in all 12 clinical participants by visual-evoked responses. Visual acuity in this group was 0.63 ± 0.19 and 0.53 ± 0.19 for the right and left eyes, respectively; most participants had mild refractive errors. All participants with achiasmia had see-saw nystagmus and no measurable stereo vision. Strabismus and abnormal head position were noted in 58% of participants. Optical coherence tomography showed optic nerve hypoplasia with associated foveal hypoplasia in four participants. In the remaining achiasmia participants, macular changes with significantly thinner paracentral inner segment (P = 0.002), wider pit (P = 0.04) and visual flattening of the ellipsoid line were found. MRI demonstrated chiasmatic aplasia in 3/12 (25%), chiasmatic hypoplasia in 7/12 (58%) and a subjectively normal chiasm in 2/12 (17%). Septo-optic dysplasia and severe bilateral optic nerve hypoplasia were found in three patients with chiasmic aplasia/hypoplasia on MRI. In this largest series of achiasmia patients to date, we found for the first time that neuronal abnormalities occur already at the retinal level. Foveal changes, optic nerve hypoplasia and the midline brain anomaly suggest that these abnormalities could be part of the same spectrum, with different manifestations of events during foetal development occurring with varying severity.

Integrating the root cause analysis to machine learning interpretation for predicting future failure

The research proposes a new model for evaluating offshore pipelines due to corrosion. The existing inspection method has an inherent limitation in reusing the primary root cause analysis data to forecast the potential loss and corrosion mitigation, particularly in the scope of data utilization. The study implements Artificial Intelligence to transfer the knowledge of failure analysis as a consideration for conducting the inspection and lowering the risk of failure. This work combines experimental and modelling methodologies to assert the actual and feasible inspection method. The elemental composition, hardness, and tensile tests are utilized to unveil the types of corrosion products and metallic properties. Scanning Electronic Microscope and Energy Dispersive X-Ray (SEM-EDX) and X-Ray Diffractometer (XRD) was utilized to assess the corrosion product and their corresponding morphology to reveal the corrosion mechanism. The Gaussian Mixture Model (GMM), aided by the Pearson Multicollinear Matrix, shows the typical risk and predicts the damage mechanism of the spool to suggest the types of mitigation scenarios for the pipeline's longevity. According to the laboratory result, the wide and shallow pit corrosion and channelling are evident. The result of the tensile and hardness test confirms the types of the API 5 L X42 PSL 1 standard material. The SEM-EDX and XRD provide a piece of clear evidence into the corrosion product are primarily due to CO2 corrosion. The silhouette score agrees well with the results of the Bayesian information criterion of GMM to show three different risk levels low, medium, and high-risk profiles. The combination of injection of chemicals such as parasol, biocide and cleaning pigging are a few solutions to address CO2 corrosion. This work can be used as a guideline for assessing and clustering the risk based on the risk-based inspection.

Analysis of the effects of isolation piles on the basal stability of foundation pits against upheaval based on continuous velocity fields.

The upper bound limit analysis method is one of the main approaches to check the basal stability of foundation pits against upheaval. However, existing studies have often failed to consider the effects of external supporting structures, including isolation piles and others, on basal stability against upheaval. This study derives a formula for the coefficient of basal stability against upheaval under the action of isolation piles by simplifying the pile-soil relationship and systematically examines the impact of isolation pile parameters on basal stability against upheaval using the theory of continuous velocity fields and the upper bound limit analysis method. A comparison of simulation results indicates that this technique can accurately identify the variation trend of basal stability against upheaval under the influence of isolation piles and achieve high calculation precision under the operating conditions of wide foundation pits and short isolation piles. Accordingly, a moderate increase in isolation pile parameters produces a significant supporting effect for narrowed foundation pits. Whereas for wide foundation pits, the supporting capacity of isolation piles can be maximized when pile length equals excavation depth.

The role of imperforate tracheary elements and narrow vessels in wood capacitance of angiosperm trees

Summary There is a broad diversity of imperforate tracheary elements (ITEs) — libriform fibers, fiber-tracheids, true tracheids and vasicentric/vascular tracheids — described thoroughly by Sherwin Carlquist. However, in a quantitative sense, the functional meaning of different ITE types present in the wood of vessel-bearing angiosperms remains unclear because very few structure–function studies measure ITEs’ properties. ITEs with abundant pits and wide pit borders — vascular tracheids, vasicentric tracheids, and true tracheids sensu Carlquist — have been shown to conduct water and, thanks to this conductive ability and the multitude of pits, they could also contribute to wood capacitance. A dataset of 30 temperate angiosperm tree species was reanalysed to record the presence/absence of true, vasicentric, and vascular tracheids including data on conduits15 fraction and vessel-conduit15 contact fraction (conduits15 were defined as cells resembling vessels and with a maximum lumen diameter of 15 μm. They encompassed narrow vessels, vasicentric tracheids, and vessel tails). The presence of tracheids, conduits15 fraction, and contact fraction had no effect on wood capacitance, except, per given wood volumetric lumen water content, species with true tracheids tended to have lower capacitance. These results suggest that the presence of tracheids or conduits15 properties do not limit wood capacitance, but the results do not exclude the potential role these cells may play in internal water dynamics.

Comparison of micromorphological changes in enamel using SEM analysis after conventional and erbium, chromium:yttrium, scandium, gallium, and garnet hard-tissue laser fissurotomy: An in vitro study.

Well articulated by John Knowles - "Everything has to evolve or else it perishes." With the paradigm shift of emphasis toward the prevention of dental caries, it has been proven that laser irradiation protects against both caries initiation and caries progression. The aim of the study was to evaluate and compare the micromorphology of caries-free extracted premolars using a Scanning electron microscope (SEM) after fissurotomy by conventional fissurotomy bur and erbium, chromium: yttrium, scandium, gallium, and garnet (ER, CR: YSGG) hard-tissue laser. Sixty caries-free premolars extracted atraumatically for orthodontic treatment were included in the study. The samples were divided into two groups randomly (Group 1: fissurotomy by bur, n = 30, and Group 2: fissurotomy by hard-tissue laser, n = 30). Each sample was further divided into halves from the occlusal surface wherein one-half of the occlusal surface received fissurotomy procedure and the other half was control. Samples were analyzed by scanning electron microscopy (SEM) for micromorphological changes. Profile image of control samples revealed the disorganization of enamel surface at the junction of fissures forming a heterogeneous tissue and agglomeration of enamel with deep pit and fissure. On the contrary, the image of experimented samples (with laser fissurotomy) showed smooth enamel surface and homogeneous enamel subsurface with wider pit and fissure owing to self-cleansing ability. On the grounds of the present study results, it could be concluded that the intervention of ER, CR: YSGG hard-tissue laser possesses self-cleansable pit and fissures for caries prevention and has the potential to irradicate the smear layer entirely for superior attachment of remineralizing agents.

Management of sacrococcygeal pilonidal sinus disease in children: A survey study in Turkey.

Sacrococcygeal pilonidal sinus disease is common in children. The disease reduces the quality of life of patients with symptoms such as pain and chronic discharge. Variable surgical techniques have been described for the treatment of pilonidal sinus disease. This study aims to evaluate clinical approach of Turkish pediatric surgeons to children with pilonidal sinus disease. Survey questions were prepared through a literature review for controversial issues. The participants were asked pre-selected and checkbox questions. The survey was sent to 450 pediatric surgeons, members of the Association of Turkey Pediatric Surgery via a link to Google Forms. Nineteen percent (88) of the members responded. Seventy five (85.2%) of the pediatric surgeons stated that they did not perform additional preoperative imaging. Surgical excision methods were preferred more than minimally invasive procedures (102 to 46). Sixty (68.2%) of the participants preferred preoperative prophylactic single dose intravenous antibiotics and postoperative oral antibiotics. Regarding the participants' practices, poor local hygiene, overweight, wide or deep sinus pit were stated as the most common causes of recurrence. Vast majority of the pediatric surgeons recommended laser epilation (%85.2) and slimming (59.1%) to patients. Various studies have been published from Turkey for pilonidal sinus disease. As seen in the current study, Turkish pediatric surgeons do not have a common opinion in pilonidal sinus disease and prefer surgical excision methods more frequently. Prospective randomized studies with bigger number of patients are required to establish common guidelines in disease management.

Design, construction and analysis for super-wide, deep and large foundation pit

Both developing and developed countries are facing a series of difficulties and challenges in the process of urbanization. In recent years, in order to alleviate the problem of urban congestion, underground space has developed rapidly, and the excavation of foundation pit is the most important step in the development of underground space. This paper takes the foundation pit of the tunnel under construction in Suzhou as a research object. The design width of the foundation pit reaches 61.5 m and the depth reaches 18 m, so it belongs to the super wide and deep foundation pit. Numerical analysis is performed by finite element software to calculate the deformation of the foundation pit. The research shows that the main problem to be solved is the deformation of the foundation pit, and the deformation of side wall of foundation pit tunnel is the most obvious. The maximum deformation of the side wall of the main tunnel and the auxiliary tunnel reached the maximum at 15 m. The maximum deformation of the main tunnel is about 1.3 cm, and that of the auxiliary tunnel is about 0.9 cm. Through targeted design and construction, the mechanical performance of the foundation pit retaining structure is optimized, and the stability of the foundation pit is strengthened. The reasonable retaining structure can ensure the good construction quality. The design and construction of the project can provide reference for related engineering construction.

ПРОБЛЕМИ, НАПРЯМКИ ТА ПЕРСПЕКТИВИ СТВОРЕННЯ І МОДЕРНІЗАЦІЇ ЗЕМЛЕРИЙНИХ МАШИН БЕЗПЕРЕРВНОЇ ДІЇ СПЕЦІАЛЬНОГО ПРИЗНАЧЕННЯ

The article addresses directions and horizons in the creation of highly efficient specialized continuously operating earthmoving machines and provided a technical proposal for the multipurpose earthmoving machine. Study subject: continuously operating earthmoving machines. Objective: To create a power-efficient special-purpose earthmoving machine. Study method: experimental. Existing dimension-types of trenching excavators allow digging lengthy excavations of the assigned profile with minor deviations from their nominal width and depth. Creating of excavations of different profiles is being achieved via machine re-equipment with different implements. A sustainable solution is to create multipurpose earthmoving machines that are capable to perform lengthy excavations of various widths and depths with the same implement and without constructional alterations. There are known machine designs for trenching on the basis of a wheeled tractor with a mounted chain-bucket implement that is able to perform the lateral oscillatory displacements in relation to the vertical axis on the hull back of the tractor. Alteration of the implements oscilative motion amplitude allows to excavate the tranches of differnt width. This is the essence of the multipurpose earthmoving machine. The existing kinematics chain sections of the implement in relation to the tractore can't ensure the consistency of the machine load due to inconsistency of the borings along the width of excavation. This leads to significant pulsation of the load on the implement, loss of the longitudinal stability and, in the end, reduces the potential productivity of the machine by half. We have performed a set of studies in creating of the multipurpose earthmoving machines (MEM). As the experimental study objects we've used physical models of the MEM implements and full-size prototypes of the machines. Results of the study experimentally confirm the possibility to create a highly productive MEM with rotary implement, which efficiently performs trenches as well as wide construction pits in the mode of reciprocating approach of the rotary implement to excavation by means of equalization and minimization of power load parameters values. KEYWORDS: EARTHMOVING MACHINE, ENERGY INTENSITY, KINEMATICS, PRODUCTIVITY, SOIL

Synthetic cell-permeable caveolin-1 scaffolding domain peptide activates phagocytosis of Escherichia coli by regulating Rab5 activity.

Caveolae are defined as 50-100nm wide pits in the plasma membrane containing oligomeric caveolin proteins. They have been implicated in endocytosis (including phagocytosis), transcytosis, calcium signalling, and numerous other signal transduction events. Caveolin-1, a major structural component of caveolae, enhances Rab5 activity. In this study, we examined the effect of a synthetic cell-permeable peptide of the caveolin-1 scaffolding domain (CSD) on phagocytosis. Treatment with the CSD peptide increased Rab5 activity, Rab5-early endosome antigen 1 (EEA1) interaction, and phagocytosis of Escherichia coli. The results suggest that the synthetic cell-permeable CSD peptide is an activator of phagocytosis.

The influence of manual and motor-manual pitting implements, pit size and quality on eucalypt performance, South Africa

Pitting is the preparation of a planting position. Various methods of pitting exist and range from manual pitting to fully-mechanised operations. Until recently, most pit preparation in South Africa was carried out manually using hand-held pitting implements (agricultural hoe, mattock, road pick) to create a 25 cm wide pit containing friable soil to a depth of 15–25 cm. However, there are several negative factors associated with manual pit preparation, such as poor ergonomics, intensive labour requirements, and inconsistent pit preparation. This has resulted in an increasing interest in semi- to fully-mechanised operations, where semi-mechanised motor-manual pitting methods are often considered more efficient and cost-effective than traditional manual operations. This study compared the performance of eucalypts planted into pits created by various pitting methods. Two trials were established with eucalypts on contrasting sites, one at Greenhill in the KwaZulu-Natal Midlands and one at Vroegeveld, Mpumalanga. Four manual implements (notch, agricultural hoe, mattock, road pick) and three different motor-manual heads (inverted A, Archimedes screw and Mondi-designed pitting head) were used to prepare and determine the effect of pit size/quality on tree survival, growth and uniformity. The notch pit implement created the smallest pit (1 L volume), whilst other implements created larger pits (4–6 L volumes). Pitting method did not have a significant effect on the success of re-establishment and subsequent tree performance on both sites (2.5 years after planting and thereafter). This indicates that for the soils tested, any possible negative tillage effects caused by any of the pitting implements did not affect the species planted. Factors such as operational costs, efficiency and ergonomics must therefore be considered to select relevant pitting methods, together with tree performance.

Craters in the vicinity of Valles Marineris region, Mars: Chronological implications to the graben and pits activities

Graben and pits are features closely associated with the Valles Marineris (VM) region on Mars. Earlier studies indicated that they are likely precursors for the VM trough formation, and thus they may assist in our understanding of how long the trough formation prevailed in the vicinity of VM. This study aims to understand how the graben and pit formation varied chronologically and spatially within a ~100 km vicinity of the VM region. We examined 1516 craters and found 48 craters that are superposed/cross-cut by graben, pits, and troughs or vice-versa with adequate ejecta or floor area for dating. Tithonium region graben and troughs cross-cut the craters around ~3.7 Ga. In the Ophir region, pits are formed on or post ~3.92 Ga at different elevations and have variable depths. Pital crater in the Ophir region interestingly hosts: 1) a broad catena ~14 km wide crosscutting its NE rim likely formed on or post to ~2.61 Ga, which inferred to be one-tenth to the adjoining Candor Chasma width of VM, 2) lobe like deposits associated with the catena emplaced over the Pital ejecta formed around ~1.14 Ga and 3) ~2 km wide pit superposed the lobe that reveals pit activity plausibly prolonged during Mid-Amazonian. Overall, our results likely point towards the contribution of graben and pits in the modification/development of peripheral areas of VM up to at least Mid-Amazonian. Thus, this study substantiated that the period and extent of graben and pit activities varied around the VM region.

Effect of polishing protocols on the surface roughness of polyetheretherketone.

The purpose of this study was to evaluate the influence of various polishing protocols on the surface roughness of polyetheretherketone (PEEK) and identify an effective polishing method of dental prostheses at the chairside. The PEEK specimens were assigned to seven groups with different protocols: no additional polishing (NT); polishing using a rubber point (C); polishing using "silky shine" (S); polishing using "aqua blue paste" (A); protocol C followed by protocol S (CS); protocol C followed by protocol A (CA); and protocol C followed by protocols S and A (CSA). The surface roughness (Sa and Ra) of the polished surfaces was measured. The surface roughness decreased in the following order of groups: NT, C, S, CS, CSA, CA, and A. In Groups C and S, wide deep pits formed by abrasive grains of SiC paper were observed, whereas only fine linear structures were observed on the surface in other groups. With respect to the polishing protocol of PEEK, clinically acceptable surface roughness was obtained using a soft polishing brush and agent for more than 3 min.